The present invention concerns generally the machining and bevelling of glasses for spectacles, and more particularly relates to a tool for the working glasses, lenses made of transparent polycarbonate plastic material.
Due to its inherent properties of transparency and breaking strength, the polycarbonate is now widely used in the production of safety spectacles, and also for ophthalmic lenses glasses. However, the machining of polycarbonate is extremely difficult since its melting temperature is relatively low, and it is therefore impossible to use standard grinding and bevelling machines for machining polycarbonate glasses, due to an excessively rapid clogging of the tools which are usually used on the standard type machine tools.
It has therefore been necessary heretofore to effect the grinding and bevelling operations with special machines for working polycarbonate lens blanks, the machines being fitted with small grinding tools having a diameter smaller than the diameter of the glass to be machined, and which grinding tools are rotated at high speed. Although such tools are usually made of tungsten carbide, their working life is undersirably very short.